Mus Demo: Demonstrate external window mode

services/ui/demo/mus_demo.h

Index: services/ui/demo/mus_demo.h
diff --git a/services/ui/demo/mus_demo.h b/services/ui/demo/mus_demo.h
index b8d5cb504c7d37291a320f879bcc7769a516f29f..f07030afd5aab738c3a3beed6106943059eaa0f5 100644
--- a/services/ui/demo/mus_demo.h
+++ b/services/ui/demo/mus_demo.h
@@ -15,6 +15,7 @@
 #include "base/macros.h"
 #include "base/timer/timer.h"
 #include "services/service_manager/public/cpp/service.h"
+#include "services/ui/public/interfaces/window_tree_host.mojom.h"
 #include "ui/aura/mus/window_manager_delegate.h"
 #include "ui/aura/mus/window_tree_client_delegate.h"
 #include "ui/display/screen_base.h"
@@ -57,12 +58,15 @@ class MusDemo : public service_manager::Service,
     explicit WindowTreeData(
         std::unique_ptr<aura::WindowTreeHostMus> window_tree_host,
         int square_size);
+    explicit WindowTreeData(mojom::WindowTreeHostFactory* factory,
+                            mojom::WindowTreeClientPtr tree_client,
+                            int square_size);
     ~WindowTreeData();
 
-   private:
     // Initializes the window tree host and start drawing frames.
     void Init(std::unique_ptr<aura::WindowTreeHostMus> window_tree_host);
 
+   private:
     // Draws one frame, incrementing the rotation angle.
     void DrawFrame();
 
@@ -72,6 +76,10 @@ class MusDemo : public service_manager::Service,
     // The Window tree host corresponding to this data.
     std::unique_ptr<aura::WindowTreeHostMus> window_tree_host_;
 
+    // When the WindowTreeData is created with WindowTreeHostFactory, this holds
+    // the Mojo pointer to the window tree host.
+    mojom::WindowTreeHostPtr host_;
+
     // Destroys itself when the window gets destroyed.
     aura_extra::ImageWindowDelegate* window_delegate_ = nullptr;